Certain types of electron tubes, e.g. color picture tubes, include a stem structure comprising a glass disk, a circular array of stiff lead-in conductors sealed through the disk, and a central opening through the disk from which an exhaust tubulation extends. It is common practice to attach a base member, usually of some type of plastic material, over the conductors and exhaust tubulation. The base member serves to protect the conductors and the exhaust tubulation, and to provide an indexing means for insertion into a mating socket.
One type of base commonly employed in the picture tube industry is the flanged base which comprises a protector cup or housing disposed over the exhaust tubulation of an electron tube stem, and a flange which extends radially outwardly from the open end of the cup. The flange is abutted against the tube stem and is provided with an array of apertures through which the conductors of the stem are disposed.
U.S. Pat. Nos. 3,278,886-Blumenberg et al. and 4,076,366-Wardell, Jr. et al. disclose flanged type bases, both of which are especially designed for high voltage applications. To this end they incorporate a tubular silo structure which surrounds one of the conductors to which high voltage is applied, and a recess in the flange of the base into which a dielectric adhesive material is molded around the high voltage conductor. Both of these features serve to increase resistance against high voltage breakdown.
In the Blumenberg et al. base, the conductors are spaced outwardly from the exhaust tubulation cup and are thus free-standing. This type of flanged base is sometimes referred to as a wafer base. In the Wardell, Jr. et al. base, the conductors lie flush against the cup in channel-like recess around the periphery of the cup. This type of flanged base is sometimes referred to as a pin-protector base.
The Wardell, Jr. et al. base is provided with a fill hole which communicates with the recess in the flange of the base so that dielectric adhesive can be injected directly into the recess through the fill hole. However, in the case of electron tubes having very small diameter stems there may not be sufficient room in the base for the fill hole. In such cases, bases more like the Blumenberg et al. base are used.
In mounting a base of the Blumenberg et al. type to an electron tube stem, it has been the practice heretofore to simply insert a quantity of dielectric adhesive material directly into the recess of the base and then apply the base to the stem. Since the dielectric adhesive material is applied to the base while it is out of contact with the stem, the result is a messy process. Alternatively, the dielectric adhesive material may be injected through the exhaust tubulation housing. In order for the material to flow along the length of the housing to the recess in the base flange and around the high voltage conductor, sufficient clearance must be provided between the exhaust tubulation and the housing wall, but this conflicts with the need to keep the exhaust tubulation as large as possible in order to facilitate the exhausting of the electron tube therethrough. The result is that often times adequate clearance for good flow of the material along the tubulation is compromised. Furthermore, the concentricity variation between the tubulation and housing may result in the greatest clearance and hence the preferential material flow path being along one side of the tubulation opposite the recess so that the flow path does not communicate with the recess in the base flange. This, of course, results in unpredictable filling of the recess and sometimes no filling at all. On the other hand, if the tubulation and housing are concentric or near concentric, there is no preferential path to material flow and the tubulation may become completely potted in the dielectric adhesive. In such cases if the base is accidentally struck, the transmitted shock to the tubulation may cause it to be fractured.
The present invention is described herein in its preferred embodiment as incorporated in a base-tube combination involving a relatively high voltage lead-in conductor with the adhesive material also being a good high voltage dielectric. However, the invention may be used in base-tube combinations where high voltage insulation is not a concern. The material may then be a simple adhesive without special high dielectric properties.